The present invention relates generally to cooling of jet engine components having a surface exposed to a hot gas flow, and more particularly to film cooling of such components. The phrase "jet engine" includes gas turbine, ramjet, and scramjet engines. Such jet engines may be used to power flight vehicles, and the gas turbine engine type of jet engine may also be used to power ships, tanks, electric power generators, pipeline pumping apparatus, etc. For purposes of illustration, the invention will be described with respect to film cooling of an aircraft gas turbine engine component using cooling air. However, it is understood that the invention is equally applicable to film cooling of other types of jet engines (such as scramjets) and/or to film cooling using other cooling fluids (such as liquid fuel).
A gas turbine engine includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a hot propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a shaft to drive the high pressure compressor. Engine thrust comes from the core engine airflow after it flows through the high pressure compressor to the combustor and is expanded past the high pressure turbine and out the exhaust nozzle. A gas turbine engine, such as an aircraft turbofan jet engine, may include other components, such as a thrust producing fan, a low pressure compressor, and a low pressure turbine.
Certain components of gas turbine engines, such as high pressure turbine rotor blades and combustor casing (or liner) walls, are subjected to hot combustion gases. Current engine designs require that such components be cooled to keep their temperatures within design limits. A known technique for cooling gas turbine engine components is film cooling of a component wall surface which is exposed to a hotter, lower static pressure gas flow. In this technique, another wall surface of the component is exposed to cooler, higher static pressure air, and a passageway is provided between the two surfaces. A cooling, thermally protective film of air thus flows out of the passageway and along the hotter surface. As future engine designs call for hotter operating temperatures, techniques are needed to improve film cooling effectiveness.